The object of this project is the development of a parathyroid hormone (PTH) bioassay based on the high sensitivity of suspensions of target-tissue-cells to hormone stimulation. Evaluation of hormone activity is done through measurement of 3'5'- cyclic- AMP accumulation. The cells are separated by mild enzymatic digestion from bone, kidney or cell cultures (osteosarcoma). Attempts will be made to establish PTH-sensitive cell lines through the culture of cells selected by affinity chromatography for PTH receptors.